Reducing Car 12VDC to 10VDC, I need help

[Ron G]

Hi---
Is there an IC that is made for car battery voltage reduction, and is
"stable" ?
If I remember, a car system goes up to about 14.4 volts while charging, then
down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

I'm an old geezer that had an associate in Electronics many decades ago, is
totally outdated, now.
Any help would be greatly appreciated.
Thanks in advance!

Ron------

 

[John Miles]

Hi---
Is there an IC that is made for car battery voltage reduction, and is
"stable" ?
If I remember, a car system goes up to about 14.4 volts while charging, then
down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

I'm an old geezer that had an associate in Electronics many decades ago, is
totally outdated, now.
Any help would be greatly appreciated.
Thanks in advance!

Ron------

Have a look at the supplies sold at http://www.mini-box.com . Chances
are, one of them will do whatever it is you're trying to do. Their
stuff works great.

-- jm

 

[Mac]

Hi---
Is there an IC that is made for car battery voltage reduction, and is
"stable" ?
If I remember, a car system goes up to about 14.4 volts while charging, then
down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

I'm an old geezer that had an associate in Electronics many decades ago, is
totally outdated, now.
Any help would be greatly appreciated.
Thanks in advance!

Ron------

What you want is readily achievable. The LM117 or LM317 can do it.

You might even be able to use the TL431. If you only need 20 mA, the TL431
might be a good choice. If you need more, the LMx17 might be a better
choice.

Take a look at the datasheets for these parts and see if you think you
need more help.

www.fairchildsemi.com/ds/TL/TL431A.pdf
http://www.national.com/pf/LM/LM117.html

Also, note that in general, people don't use "mils" as a measure of
current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated
"mA."

--Mac

 

[Glenn Gundlach]

Hi---
Is there an IC that is made for car battery voltage reduction, and is
"stable" ?
If I remember, a car system goes up to about 14.4 volts while charging, then
down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

I'm an old geezer that had an associate in Electronics many decades ago, is
totally outdated, now.
Any help would be greatly appreciated.
Thanks in advance!

Ron------

You want a low dropout regulator. National fixed voltage LM2930, LM2940
and if you want adjustable, LM2941 will suit you just fine.
GG

 

[CF]

Also, note that in general, people don't use "mils" as a measure of

current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated
"mA."

People do indeed say "mils" when speaking of mA. They =write= mA,
but =say= "mils". It's pretty hard to get "mils - mA" mixed up
with "mils - thousandths of an inch" in a discussion

 

[Luhan Monat]

People do indeed say "mils" when speaking of mA. They =write= mA,
but =say= "mils". It's pretty hard to get "mils - mA" mixed up
with "mils - thousandths of an inch" in a discussion

I agree, 'mils' is used between engineers in conversation, so is 'mA'.

 

[martin griffith]

You want a low dropout regulator. National fixed voltage LM2930, LM2940
and if you want adjustable, LM2941 will suit you just fine.
GG

on
http://www.fordemc.com/docs/p7.html

ES-XW7T-1A278-AB/C: Component/Subsystem EMC Requirements and Test
Methods

Part 3 Figure CI 240 -1, Load Dump Test



martin

After the first death, there is no other.
(Dylan Thomas)

 

[[email protected]]

If I remember, a car system goes up to about 14.4 volts while charging,
then down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

It can go down lower than 13.8 V, if you're talking about when the
engine's not running, or if the engine is running but there is a high
electrical load. A fully-charged car battery at no load is about 12.6 V;
you'll get less than that at the cigarette lighter socket and less still
if someone is sitting there with the key off and the radio and dome light
on, etc. During cranking, most cars go as low as 9.5 V or so at the
battery and still start. I have heard a suggestion that when designing
for automotive use, a device should "work" over a 10 V to 15 V range,
and "survive" 0 V to something well over 15 V, like maybe 30 V or more.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

I second the LM317 suggestion. That's a linear regulator that is good
for at least 1 amp (in the TO-220 package) with a heat sink; you may not
need a heat sink or only a very small one for your small demand. IIRC
the maximum drop through it is about 1.3 V, so for your 10 V
requirement, the input has to be at 11.3 V or more. If the input is
less than that, you'll probably get whatever's at the input minus 1.3 V,
unregulated. In other words, this device won't "work" down to 10 V, but
that might not be important to you.

The other option is a DC-DC converter. This is a little brick that
typically takes a wide range of DC input, chops it into AC, runs it
through a transformer, rectifies the AC back into DC, and regulates it.
This will be more expensive than the linear regulator, but will work
over a wider range of input voltages. The other problem is that a
10 V output is hard to come by; you could use two 5 V converters and
wire the outputs in series, or use a 12 V output one and follow it
with a linear regulator. Basically, what this buys you is operation
over a wider input voltage range, and a little more isolation from the
car's electrical system.

I'm an old geezer that had an associate in Electronics many decades ago,
is totally outdated, now.

Yeah... They changed which end of a soldering iron to pick up and
everything.

Matt Roberds

 

[mike]

Hi---
Is there an IC that is made for car battery voltage reduction, and is
"stable" ?
If I remember, a car system goes up to about 14.4 volts while charging, then
down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

I'm an old geezer that had an associate in Electronics many decades ago, is
totally outdated, now.
Any help would be greatly appreciated.
Thanks in advance!

Ron------

Before you do anyting automotive, read this.
http://www.littelfuse.com/data/en/Application_Notes/an9312.pdf

I'm not familiar with the numeric parameters associated with "nice
smooth".

If you expect to get 10V out with ALL automotive conditions, you won't
get there with a simple linear regulator, LDO or otherwise.

Whatever you do, make sure you have LOTS of transient protection on the
input.

I always caution novice auto power supply designers to weigh the cost of
the device they're powering against the money you save building your own
supply. Risking a $2K laptop on a $20 savings in power supply design
is false economy. YMMV.

There are also a bunch of other automotive considerations depending on
what you're trying to do. For example, I've never achieved a power
suppy for my mp3 player that didn't have excessive ignition and
alternator whine sneaking thru ground loops.

mike



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[Mac]

People do indeed say "mils" when speaking of mA. They =write= mA,
but =say= "mils". It's pretty hard to get "mils - mA" mixed up
with "mils - thousandths of an inch" in a discussion

I have never heard anyone say "mil" when talking about milliamps. Could be
lack of experience or exposure on my part.

In any event, I believe my comment still applies to written communication.

--Mac

 

[John Miles]

I always caution novice auto power supply designers to weigh the cost of
the device they're powering against the money you save building your own
supply. Risking a $2K laptop on a $20 savings in power supply design
is false economy. YMMV.

Which is why I pointed him at mini-box.com. Whatever your automotive
power problem, it's safe to say that an LM317T is absolutely NOT the
solution.

-- jm

 

[Fred Bloggs]

Is there an IC that is made for car battery voltage reduction, and is
"stable" ?
If I remember, a car system goes up to about 14.4 volts while charging, then
down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase
winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the
exact mills for sure yet)

That would be something like the LM2941C, this is designed to withstand
the automotive load dump as well as to provide other excellent
performance characteristics, such as requiring a mere 100mV input-output
differential at your low load levels. See
http://cache.national.com/ds/LM/LM2941.pdf and page 8. You will want to
place a high voltage diode in series between VBATT and Vin to the
regulator- most applications use 1000PIV- to guard against the
occasional negative transient on the BATT line. Your regulator will
dropout during extreme cranking load- but otherwise should work peachy
keen in every other circumstance.

 

[Fred Abse]

I have never heard anyone say "mil" when talking about milliamps. Could be
lack of experience or exposure on my part.

"It's volts that jolts, but it's mils that kills"

 

[jtaylor]

Also, note that in general, people don't use "mils" as a measure of
current. A "mil" is a thousandth of an inch.

mil = 202.25 arc-seconds, roughly.

 

[Paul Burke]

mil = 202.25 arc-seconds, roughly.

'thou' in British usage. "A book of verse, a flask of wine, and 25.4
micrometres" doesn't quite have the same ring to it.

Paul Burke